For example, it is known that certain regions of a gas turbine engine—particularly those nearest the air intake—may be susceptible to ice formation on components such as guide vanes, struts and duct walls. Icing may occur at any time, whether or not the engine is running, if the atmospheric conditions are appropriate. When the engine is running, icing may occur during ground running, at idle or at higher engine speeds, as well as during operation in flight. In such circumstances ice may build up on, and then be shed from, these components, and the ice may cause damage to other components further downstream in the engine. The risk of icing is exacerbated when the design of the engine is such that the fan or low-pressure compressor imparts only a small temperature rise to the air. If ice has built up on components of the engine while it is not running, it may or may not be shed from the engine immediately on starting.
In order to avoid ice build-up on vulnerable components it is known to make these components hollow, so that hot air from the combustor or elsewhere in the engine can be used to warm the component and thereby prevent icing. However, hollow components increase engine complexity, and consequently manufacturing costs and timescales. In cases where components have complicated 3D geometry for aerodynamic reasons, as is increasingly common, it may be difficult or impossible to make them hollow. Components, which move or rotate (such as variable vanes), add yet more complexity and potential leakage, because the hot air flow must be provided through a rotating spindle to the component.
Furthermore, this method of heating the component relies principally on heat soak through the component walls. It is therefore relatively inefficient, and has the further disadvantage that it tends to heat the whole component, not only that part of it susceptible to icing.
It would therefore be desirable to have an improved method of preventing icing of components, which overcomes the disadvantages of known techniques.